Plasma melting method and plasma melting furnace

Abstract

A plasma melting furnace has a melting chamber having an anode torch and a cathode torch made of graphite and having a electric conductor disposed on the bottom thereof. When the furnace is operated, the anode torch, having an inflow of electrons, which forms an unstable plasma arc is contacted with the electric conductor and is not used, while the cathode torch, having an outflow of electrons, which forms a stable plasma arc, is utilized for heating, whereby the furnace can be stably and continuously operated. Thus, since the cathode torch which is used is not heated so much and the anode torch, which is liable to be heated to a great degree, is not used, the electrode consumption rate can be greatly reduced.

What is claimed is: 
     
       1. A plasma melting method for a plasma melting furnace comprising a melting chamber having a lower region and an upper region, an anode torch having an upper and a lower end, a cathode torch, and an electric conductor located in the lower region of the melting chamber, said method adapted for use during conditions including starting the furnace, increasing the temperature of the furnace, and charging a material to be melted in the furnace, said method comprising the steps of: moving the anode and cathode torches into contact with the electric conductor to initiate a furnace start; and   moving the cathode torch out of contact with the electric conductor to at least one position in the upper region of the melting chamber, generating a plasma arc between the cathode torch and the electric conductor.   
     
     
       2. A plasma melting method as set forth in claim 1, wherein said at least one position of the cathode torch in the upper region of the melting chamber includes a preparatory arc position and a heating arc position, said cathode torch moving to said preparatory arc position to begin generation of the plasma arc between the cathode torch and the electric conductor, and said cathode torch moving to said heating arc position after confirmation of the melting of the electric conductor, to heat the interior of the furnace, said heating arc position being a greater distance from the electric conductor than the preparatory arc position. 
     
     
       3. A plasma melting method for a plasma melting furnace comprising a melting chamber having a lower region and an upper region, an anode torch having an upper and a lower end, a cathode torch, and an electric conductor located in the lower region of the melting chamber, said method comprising the steps of: moving the anode and cathode torches into contact with the electric conductor to initiate a furnace start;   moving the cathode torch out of contact with the electric conductor, to a preparatory arc position for beginning generation of a plasma arc between the cathode torch and the electric conductor; and   after confirmation of the melting of the electric conductor, moving the cathode torch to a heating arc position to heat the interior of the furnace, said heating are position being a greater distance from the electric conductor than said preparatory arc position.   
     
     
       4. A plasma melting method as set forth in claim 3, further comprising the steps of: heating the atmosphere temperature in the furnace to between approximately 900° and 1,000° C.,   after confirmation of the melting of the electric conductor in a region near the anode torch, the anode torch is moved to a preparatory arc position to generate a plasma arc between the anode torch and the electric conductor, and   after confirmation of the spreading of the melting of the electric conductor in the region near the anode torch, the anode torch is moved to a heating arc position for heating the gas atmosphere in the furnace, said heating arc position being a greater distance from the electric conductor than the preparatory arc position.   
     
     
       5. A plasma melting method as set forth in claim 4, wherein if the plasma arc respectively generated by either the anode torch or the cathode torch is interrupted when the anode and cathode torches are respectively moved during the charging of ash into the furnace, the charging of ash is interrupted and the anode and cathode torches are moved into contact with the electric conductor or the molten slag, whereupon the cathode torch is moved out of contact with the electric conductor to generate a plasma arc between the cathode torch and the electric conductor, to maintain the temperature in the furnace at between approximately 900° and 1,000° C., and thereafter the anode torch is moved out of contact with the electric conductor to generate a plasma arc between the anode torch and the electric conductor, and charging of ash into the furnace is restarted. 
     
     
       6. A plasma melting method for a plasma melting furnace comprising a melting chamber having a lower region and an upper region, an anode torch having an upper and a lower end, a cathode torch, and an electric conductor located in the lower region of the melting chamber, said method comprising the steps of: moving the anode and cathode torches into contact with the electric conductor to initiate a furnace start;   moving the cathode torch out of contact with the electric conductor to a first position from the electric conductor, to generate a plasma arc and increase the atmosphere temperature in the furnace to between approximately 900° C. and 1,000° C.;   after confirmation of the melting of the electric conductor in a region near the anode torch, moving the anode torch out of contact with the electric conductor to a preparatory arc position, to generate a plasma arc; and   after confirmation of the spreading of the melting of the electric conductor in the region near the anode torch, moving the anode torch to a heating arc position, to heat the gas atmosphere in the furnace, said heating arc position being a greater distance from the electric conductor than the preparatory arc position.   
     
     
       7. A plasma melting furnace comprising: a melting chamber having a lower region and an upper region, an electric conductor located in the lower region of the melting chamber,   a movable anode torch made of graphite and having upper and lower ends, said anode torch movable to position wherein the lower end of the anode torch is in contact with the electric conductor; and   at least one movable cathode torch made of graphite, said at least one cathode torch movable to a position in the upper region of the melting chamber to generate a plasma arc between the cathode torch and the electric conductor.   
     
     
       8. A plasma melting method for a plasma melting furnace comprising a melting chamber having a lower region and an upper region, an anode torch made of graphite and having upper and lower ends, and at least one cathode torch made of graphite, and an electric conductor located in the lower region of the melting chamber, said plasma melting method adapted for use during conditions including starting the furnace, increasing the temperature of the furnace, and charging a material to be melted in the furnace, said method comprising the steps of: moving the anode torch and the at least one cathode torch into contact with the electric conductor;   moving the at least one cathode torch to the upper region of the melting chamber to generate a plasma arc between the cathode torch and the electric conductor.   
     
     
       9. A plasma melting method as set forth in claim 8, characterized in that the length of a plasma arc generated between the electric conductor and the at least one cathode torch is controlled on the basis of a potential difference applied between the at least one cathode torch and the electric conductor rendered conductive through the anode torch. 
     
     
       10. A plasma melting furnace as set forth in claim 7, characterized in that the at least one cathode torch is disposed substantially in the middle of the melting chamber. 
     
     
       11. A plasma melting furnace as set forth in claim 7, wherein the anode torch is disposed closer than the at least one cathode torch, to a charging port for a material to be molten. 
     
     
       12. A plasma melting furnace as set forth in claim 10, wherein the anode torch is disposed closer than the at least one cathode torch, to a charging port for a material to be molten. 
     
     
       13. A plasma melting furnace as set forth in claim 7, wherein said furnace has one anode torch and a plurality of cathode torches. 
     
     
       14. A plasma melting furnace as set forth in claim 10, wherein said furnace has one anode torch and a plurality of cathode torches. 
     
     
       15. A plasma melting furnace as set forth in claim 11, wherein said furnace has one anode torch and a plurality of cathode torches. 
     
     
       16. A plasma melting furnace as set forth in claim 12, wherein said furnace has one anode torch and a plurality of cathode torches. 
     
     
       17. A plasma melting furnace as set forth in claim 7, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the at least one cathode torch and the electric conductor rendered conductive through the anode torch, the length of a plasma arc generated between the electric conductor and the at least one cathode torch controlled on the basis of the potential difference. 
     
     
       18. A plasma melting furnace as set forth in claim 10, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the at least one cathode torch and the electric conductor rendered conductive through the anode torch, the length of a plasma arc generated between the electric conductor and the at least one cathode torch controlled on the basis of the potential difference. 
     
     
       19. A plasma melting furnace as set forth in claim 11, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the at least one cathode torch and the electric conductor rendered conductive through the anode torch, the length of a plasma arc generated between the electric conductor and the at least one cathode torch controlled on the basis of the potential difference. 
     
     
       20. A plasma melting furnace as set forth in claim 12, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the at least one cathode torch and the electric conductor rendered conductive through the anode torch, the length of a plasma arc generated between the electric conductor and the at least one cathode torch controlled on the basis of the potential difference. 
     
     
       21. A plasma melting furnace as set forth in claim 13, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the at least one cathode torch and the electric conductor rendered conductive through the anode torch, the length of a plasma arc generated between the electric conductor and the at least one cathode torch controlled on the basis of the potential difference. 
     
     
       22. A plasma melting furnace as set forth in claim 14, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the at least one cathode torch and the electric conductor rendered conductive through the anode torch, the length of a plasma arc generated between the electric conductor and the at least one cathode torch controlled on the basis of the potential difference. 
     
     
       23. A plasma melting furnace as set forth in claim 15, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the at least one cathode torch and the electric conductor rendered conductive through the anode torch, the length of a plasma arc generated between the electric conductor and the at least one cathode torch controlled on the basis of the potential difference. 
     
     
       24. A plasma melting furnace as set forth in claim 16, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the at least one cathode torch and the electric conductor rendered conductive through the anode torch, the length of a plasma arc generated between the electric conductor and the at least one cathode torch controlled on the basis of the potential difference. 
     
     
       25. A plasma melting furnace as set forth in claim 10, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       26. A plasma melting furnace as set forth in claim 11, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       27. A plasma melting furnace as set forth in claim 12, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       28. A plasma melting furnace as set forth in claim 13, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       29. A plasma melting furnace as set forth in claim 14, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       30. A plasma melting furnace as set forth in claim 15, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       31. A plasma melting furnace as set forth in claim 16, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       32. A plasma melting furnace as set forth in claim 17, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       33. A plasma melting furnace as set forth in claim 18, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       34. A plasma melting furnace as set forth in claim 19, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       35. A plasma melting furnace as set forth in claim 20, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       36. A plasma melting furnace as set forth in claim 21, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       37. A plasma melting furnace as set forth in claim 22, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       38. A plasma melting furnace as set forth in claim 23, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch. 
     
     
       39. A plasma melting furnace as set forth in claim 24, wherein said furnace further comprises at least one potentiometer for providing a potential difference between the anode torch and said at least one cathode torch.